Development of deoxidation process for off-grade titanium sponge using magnesium metal with wire mesh strainer type of crucible

In this study, the deoxidation process for off-grade titanium (Ti) sponge using magnesium (Mg) metal with a wire mesh strainer type of crucible was developed. Ti hydride (TiH2) feedstock, which was prepared by hydrogenating off-grade Ti sponge, was deoxidized using Mg in a molten magnesium chloride–potassium chloride salt at 933 K under an argon and 20% hydrogen (H2) mixed gas atmosphere. After deoxidation, the residual Mg-containing salt was separated in situ from the crucible to investigate the feasibility of minimizing salt loss during the leaching and production of pure TiH2. The results showed that the presence of residual Mg-containing salt inside the crucible strongly influenced whether a mixture of Ti and TiH2 or pure TiH2 was produced. When the salt was not sufficiently separated, a mixture of Ti and TiH2 was obtained and its oxygen (O) concentration was 0.121 mass% under certain conditions. Meanwhile, pure TiH2 was obtained by increasing the H2 gas flow rate during deoxidation. Therefore, these results demonstrate that the decrease of O concentration to below 0.180 mass% and the minimal loss of the salt are feasible.

Titanium (Ti) is used in aerospace, biomedical, and chemical processing applications because it and its alloys exhibit excellent properties such as high specific strength, corrosion resistance, and biocompatibility.Accordingly, the demand for Ti, particularly for aerospace applications, continues to increase 1-3 .However, the global production of Ti is lower than that of iron (Fe) and aluminum (Al) 4 .The main reasons for the low production volume of Ti are the low productivity and high processing costs of conventional Ti production processes 5 .
In conventional Ti production, the Kroll process, several factors are responsible for its low productivity and high processing cost, such as a batch-type operation and the long processing time 6,7 .Notably, off-grade Ti sponge is generated during the Kroll process 8,9 .It is estimated that 10-20% of the total production volume of Ti sponge 10 .This indicates that the high processing costs can be reduced by developing an efficient utilization method for off-grade Ti sponge.When off-grade Ti sponge can be utilized in Ti ingot production, it not only reduces the high processing costs of Ti but also compensates for the low Ti production volume.In addition, this can decrease carbon dioxide emissions by 95.4% because upgrading low-grade Ti ore and the Kroll process are not required 11 .Therefore, the recycling of off-grade Ti sponge is important.
The main challenge associated with the recycling of off-grade Ti sponge is the removal of major impurities such as oxygen (O) and Fe.These impurities negatively affect the mechanical properties of the final product and are almost impossible to remove from Ti using conventional remelting techniques.As a result, in modern industrial practice, off-grade Ti sponge is cheaply used as an additive in the steel industry.However, when the O concentration in off-grade Ti sponge can be lowered to below 0.180 mass%, which is the American Society for Testing Materials (ASTM) criteria for Grade 1 Ti 12 , off-grade Ti sponge can be utilized in Ti alloy production.
Although Fe cannot be removed directly from off-grade Ti sponge, it can be used as a β-stabilizer in β-Ti alloys 13,14 .Therefore, to recycle off-grade Ti sponge for use in Ti production, a deoxidation process to decrease its O concentration to below 0.180 mass% is necessary.
Numerous methods for deoxidation of Ti using various reducing agents have been proposed.Due to the high affinity of O to Ti, most reducing agents used in the proposed deoxidation processes are limited to rare-earth elements, such as holmium (Ho) 15 , yttrium (Y) 16,17 , and lanthanum (La) 18 , calcium (Ca) [19][20][21][22][23][24][25][26][27][28][29] , and electrons [30][31][32] .However, magnesium (Mg), which is the cheapest among the metallic reducing agents, is not suitable as a reducing agent for deoxidation of Ti.This is because the O concentration in Ti by Mg/magnesium oxide (MgO) equilibrium at 1200 K is approximately 2 mass% in the standard state 33 , which is significantly higher than the 0.180 mass%.
In recent years, several studies have been conducted on the deoxidation of Ti using Mg [34][35][36][37][38][39][40] to increase its capability to decrease the O concentration in Ti.Some of these studies proposed the promising hydrogen (H) assisted Mg reduction process for the deoxidation of Ti using Mg [34][35][36] , in which the magnesiothermic reduction of Ti is conducted in a hydrogen gas (H 2 ) atmosphere.In this process, the O concentration in Ti is decreased to 0.0503 mass% when deoxidation is performed at 1023 K for 12 h in an H 2 gas atmosphere 34 .This indicates that the O concentration in Ti can satisfy the ASTM criteria for Grade 1 Ti by the deoxidation even when Mg is used as the reducing agent under a high hydrogen chemical potential.
To develop a novel and efficient recycling process for off-grade Ti sponge, the deoxidation of off-grade Ti sponge using Mg in argon (Ar) and H 2 mixed gas at 933-993 K was investigated by the authors 41,42 .To increase the activity of hydrogen (a H ) in the reaction system and reaction rate, titanium hydride (TiH 2 ) powder produced by hydrogenating an off-grade Ti sponge was used as the feedstock for deoxidation.
However, several drawbacks remain, such as the loss of residual Mg-containing salts during leaching and the production of a mixture of Ti and TiH 2 instead of pure TiH 2 .The production of TiH 2 is preferred to that of Ti, considering the sintering process after the deoxidation process.This is because the sintered compact using TiH 2 powder has a higher sintered density than that using pure Ti powder, which improves the mechanical properties of the final Ti product 43,44 .However, in the authors' previous studies 41,42 , a mixture of Ti and TiH 2 was produced after the deoxidation.This was because TiH 2 feedstock inside the salt was dehydrogenated during the deoxidation owing to the low hydrogen partial pressure ( p H 2 ) inside the salt.Therefore, the development of a method for the production of pure TiH 2 is required even after the deoxidation.
In addition, salt loss was unavoidable because the salt was removed during subsequent leaching to recover the deoxidized product.It is worth noting that separating the residual Mg-containing salt from the deoxidized product before leaching can significantly reduce the amount of acid waste solution and the residual Mg-containing salt can be reused for deoxidation.Furthermore, reducing the amount of residual Mg-containing salt to be removed shortens the leaching time; thus, O contamination during leaching can be reduced.Therefore, to simultaneously overcome these drawbacks, the separation of residual Mg-containing salt during deoxidation is necessary.
In this study, a deoxidation process for off-grade Ti sponge was developed with the aim of decreasing the O concentration to below 0.180 mass%, minimizing the loss of residual Mg-containing salt, and producing pure TiH 2 .The influence of the reaction time on the O concentration in the residue was investigated.After deoxidation, the feasibility of separating the residual Mg-containing salt was investigated via in situ separation by lifting a wire mesh strainer type of crucible.Furthermore, the influences of the H 2 gas flow rate, hydrogenation temperature, and draining time on the separation of the residual Mg-containing salt and the production of pure TiH 2 were systematically investigated.Figure 1 shows a flowchart of the deoxidation process for off-grade Ti sponge using Mg with a wire mesh strainer type of crucible in an Ar and 20% H 2 mixed gas atmosphere.

Deoxidation of Ti using Mg in an Ar and H 2 mixed gas atmosphere
The chemical potential diagram of the Ti-O-H system at 973.15 K was plotted in Fig. 2 using the Chesta software 45 and various thermodynamic data 34,46,47 .The ordinate denotes the oxygen partial pressure ( p O 2 ) and the abscissa denotes the p H 2 .
The stability regions of the Ti-O solid solutions are divided by dashed lines depending on the O concentration in Ti (s).The stability region of Ti-0.6 mass% O is located in the p O 2 range of 6.5 × 10 −54 -8.7 × 10 −54 atm and the p H 2 range below 5.8 × 10 −3 -5.9 × 10 −3 atm.The p O 2 by the Mg (l)/MgO (s) equilibrium is 6.5 × 10 −54 atm at 973.15 K under the standard state.This p O 2 is located in the stability region of Ti-0.6 mass% O at p H 2 below 5.8 × 10 −3 atm.Therefore, when Ti is deoxidized using Mg at p O 2 below 5.8 × 10 −3 atm under a standard state, the O concentra- tion in Ti will be 0.6 mass%, which is greater than 0.180 mass%.This indicates that the O concentration in Ti cannot be decreased to below 0.180 mass% when Ti is deoxidized using Mg without H 2 gas under standard state.
However, there are two methods to decrease the O concentration in Ti to below 0.180 mass%, even when Mg is used as the reducing agent.One is to decrease the activity of MgO (a MgO ).For example, when a MgO is decreased to 0.1, the p O 2 by Mg (l)/MgO (s) equilibrium decreases to 6.51 × 10 −56 atm, as shown in Fig. 2.This p O 2 is located in the stability region of Ti-0.05 mass% O even at p H 2 below 5.6 × 10 −3 atm.Therefore, although Mg is used as a reducing agent, the O concentration in Ti can be decreased to 0.05 mass% when the removal of the produced MgO during the deoxidation of Ti is maintained via chemical reactions or electrolysis 33,37,38,48 .
Another method is utilizing H 2 to deoxidize Ti.As shown in Fig. 2, when p O 2 is 6.51 × 10 −54 atm determined by Mg (l)/MgO (s) equilibrium at 973.15 K, the stability regions of TiH 0.290 O 0.005 (s), TiH 0.339 O 0.005 (s), and TiH 0.388 O 0.005 (s) are located at p O 2 above 5.8 × 10 −3 atm, 2.6 × 10 −2 atm, and 3.6 × 10 −2 atm, respectively.That is, when the p H 2 is maintained above 5.8 × 10 −3 atm and Mg is used as a reducing agent, the p O 2 by Mg (l)/MgO (s) equilibrium is located in the stability regions of TiH 0.290 O 0.005 (s), TiH 0.339 O 0.005 (s), and TiH 0.388 O 0.005 (s) with an O concentration of 0.166 mass%.Although only a few types of TiH x O y are plotted owing to the lack of

TiH 2 production in an Ar and H 2 mixed gas atmosphere
To investigate the feasibility of TiH 2 production, a thermodynamic analysis of the hydrogenation reaction is necessary.The production of TiH 2 by the hydrogenation of Ti with H 2 gas is described by Eq. (1) 46 .In addition, p H 2 by Ti (s)/TiH 2 (s) equilibrium can be expressed as shown in Eq. (2) using Eq.(1).
(1) www.nature.com/scientificreports/ In the previous study, although the TiH 2 feedstock was deoxidized using Mg in an Ar and 20% H 2 mixed gas atmosphere at 933 K, a mixture of Ti and TiH 2 was produced instead of pure TiH 2 41 .The TiH 2 feedstock was deoxidized in a molten mixture of Mg and magnesium chloride (MgCl 2 )-potassium chloride (KCl).This indicates that the p H 2 inside the molten Mg and salt was low, resulting in the dehydrogenation of TiH 2 during deoxidation.As a result, the production of a mixture of Ti and TiH 2 was unavoidable.It has also been reported that the diffusion of H 2 gas to the Ti sub-hydride (TiH x with x < 2) is impeded when MgCl 2 covers the Ti subhydride powder 49 .Therefore, to increase the phase ratio of TiH 2 in the mixture of Ti and TiH 2 , the p H 2 inside the molten salt should be maintained at a high value during deoxidation or the molten salt should be separated during deoxidation enabling to expose of the deoxidized product to a high p H 2 .
In this study, a wire mesh strainer type of crucible was used for deoxidation.Deoxidation was performed by lowering the crucible, which contained the TiH 2 feedstock prepared using off-grade Ti sponge, into the molten salt.After deoxidation was finished, the crucible was slightly raised above the surface of the molten salt and maintained for a certain period to separate the molten salt from the crucible and expose the feedstock to a high p H 2 .

Methods
Figure 3a shows the schematic of the experimental apparatus used in this study.In addition, Fig. 3b-g show photographs of parts of the Fe crucible assembly and samples used in the experiments.As shown in Fig. 3c, the TiH 2 powder produced from off-grade Ti sponge was used as the feedstock for deoxidation.To prepare the TiH 2 feedstock, off-grade Ti sponge (VSMPO-AVISMA Corporation) was hydrogenated at 973 K for 2 h in an H 2 gas atmosphere at MTIG Co., Ltd.After hydrogenation, the TiH 2 feedstock was pulverized using a mortar and pestle, followed by sieving.The particle size of TiH 2 feedstock used for deoxidation was 150-300 μm.
Before deoxidation, the salt was dried and pre-melted to remove H 2 O from the chemical reagents.MgCl 2 (anhydrous, purity > 97.0%, Wako Pure Chemical Corporation) and KCl (anhydrous, purity > 99.0%, KOJUNDO Chemical Laboratory Co., Ltd.) were dried at 453 K for 72 h in a vacuum oven (VOS-601SD, EYELA).Subsequently, the dried MgCl 2 and KCl were placed inside a reactor, while being contained within an Fe container The interior of the reactor was evacuated for 15 min at 298 K and then filled with an Ar and 20% H 2 mixed gas to an internal pressure of 1 atm.The internal pressure of the reactor was maintained at 1 atm until the end of the experiment by constantly flowing mixed gas into the reactor.After controlling the atmosphere, the reactor was heated to 933 K.After 1 h at 933 K, the crucible was immersed in the molten salt by lowering it to 1 mm www.nature.com/scientificreports/above the bottom of the Fe container for deoxidation of the TiH 2 feedstock.After deoxygenation for the duration of 1-24 h, the crucible was lifted to 30 mm above the bottom of the Fe container to be positioned above the molten salt and held for 30 min or 3 h to drain the residual Mg-containing salt from the crucible through the Ti mesh.Subsequently, the crucible was lifted to 329 mm above the bottom of the Fe container, and the reactor was cooled to 298 K.
To hydrogenate deoxidized TiH 2 feedstock, the temperature was held for 24 h after the crucible was lifted to 329 mm above the bottom of the Fe container where the temperature was 773 K, as shown in Fig. 4. In a different manner, after drainage of the residual Mg-containing salt, the crucible was lifted to 269 mm above the bottom of the Fe container where the temperature was 873 K and held for 24 h.The reactor was then cooled to 298 K.
After the experiments, the residual Mg, MgCl 2 , KCl, and MgO produced inside the crucible were removed by HCl leaching, as shown in Fig. 5. HCl leaching was performed using 1 L of 10% HCl solution at 298 K for 1 h without stirring and by blowing Ar gas into a jacketed reaction vessel.Subsequently, the residues were filtrated and washed with deionized (D.I.) water, followed by washing with acetone.The obtained residues were leached again using 1 L of 10% HCl solution at 298 K for 30 min with stirring at 150 rpm and by blowing Ar gas into a jacketed reaction vessel.After leaching, the residue was filtrated and washed with D.I. water, followed by washing with acetone.
The concentrations of O in the samples were analyzed using an N/O/H determinator (TCH600, LECO Corporation).The crystalline phases of the samples were identified using X-ray diffractometer (XRD: X'Pert MPD, PHILIPS, Cu-Kα radiation).

Deoxidation of TiH 2 feedstock
Figure 6 shows the TiH 2 , produced from off-grade Ti sponge by hydrogenation at 973 K for 2 h in an H 2 gas atmosphere according to Eq. (1).The concentration of O in the TiH 2 feedstock was 1.28 mass%, as listed in Table 1.
In addition, Table 1 lists the experimental conditions for the deoxidation of TiH 2 feedstock using Mg in an Ar and 20% H 2 mixed gas atmosphere.In deoxidation, the mass ratios of Mg to feedstock (r Mg/feedstock ) and salt to feedstock (r salt/feedstock ) were maintained at 1 and 20, respectively.r salt/feedstock and r Mg/feedstock were calculated using Eqs.( 3) and (4), respectively.In Eqs. ( 3) and (4), w salt , w TiH 2 _feed , and w Mg refer to the weights of the salt, TiH 2 feedstock, and Mg used, respectively.
(3) r salt/feedstock = w salt g /w TiH 2 _feed (g) (4) r Mg/feedstock = w Mg g /w TiH 2 _feed (g) Figure 5. Flowchart of the experimental procedure for the deoxidation of off-grade Ti sponge using Mg metal and the production of TiH 2 powder in an Ar + 20% H 2 gas atmosphere.Figure 7a-c show that the residual Mg-containing salt drained through the Ti mesh at the bottom of the crucible when the crucible was lifted to 30 mm above the bottom of the Fe container.The material remaining in the crucible was removed by HCl leaching according to the reactions shown in Eqs. ( 5) and ( 6) 50 .After HCl leaching, the deoxidized product was obtained as a fine powder, as shown in Fig. 7d,e.
As shown in Table 1, the O concentration in the feedstock of 1.28 mass% was decreased with an increasing deoxidation time.As a result, the lowest O concentration was 0.121 mass% when the TiH 2 feedstock was deoxidized for 24 h.
As shown in Fig. 2, the equilibrium concentration of O in the deoxidized product was determined by the p O 2 , and p O 2 was determined by the Mg (l)/MgO (s) equilibrium as a function of the activity of Mg (a Mg ) and a MgO in the reaction system.In this study, a Mg was assumed to be unity during deoxidation.This is because, when the r Mg/feedstock was maintained at 1, the amount of Mg used was 51 times larger than the amount required to reduce O in the TiH 2 feedstock.The mass ratio of the Mg used to the Mg required was calculated using Eqs.( 7)-( 9).In addition, a MgO was assumed to be unity because the solubility of MgO in MgCl 2 at 1003 K and 1073 K were reported to be only 0.36 mol% and 0.63 mol%, respectively [51][52][53] .When considering the value of r salt/feedstock and the amount of the MgO produced by complete deoxidation and MgCl 2 used, the mol% of MgO in MgCl 2 would be 0.51 mol%, which is greater than 0.36 mol%.In addition, the actual mol% of MgO in MgCl 2 would be larger than 0.51 mol% when the generation of MgO by reacting MgCl 2 with H 2 O absorbed to MgCl 2 owing to its hygroscopic property 54,55 .Moreover, because the MgO solubility in MgCl 2 decreases with a decreasing temperature, the MgO solubility in MgCl 2 at 933 K is expected to be lower than that in MgCl 2 at 1003 K, 0.36 mol%.
In Eqs. ( 7)-( 9), w Mg required , C O, in the feedstock , w TiH 2 _feed , m O , m Mg , r Mg used/Mg required , and w Mg refer to the calculated weight of Mg to deoxidize O in the TiH 2 feedstock, initial O concentration of the feedstock used (mass%), weight of the TiH 2 feedstock used (g), atomic mass of O (15.999 g•mol −1 ), atomic mass of Mg (24.305 g•mol −1 ), ratio of the amount of Mg used to Mg required, and weight of Mg used (g), respectively.
The thermodynamic analysis results presented in Fig. 2 show that Ti containing O of 0.166 mass% can be obtained under the standard state when the TiH 2 is deoxidized using Mg at 973 K under a high hydrogen chemical potential.Although a detailed evaluation of the equilibrium concentration of O in Ti at 933 K was difficult owing to the lack of thermodynamic data, the experimental results, such as the deoxidized product obtained containing O of 0.121 mass%, demonstrated that the experimental results agreed with the thermodynamic analysis results.Consequently, these results show that the O concentration in the off-grade Ti sponge could be decreased to below 0.180 mass% by deoxidizing TiH 2 using Mg at 933 K in an Ar and 20% H 2 mixed gas atmosphere.
Figure 8 shows the XRD analysis results of the deoxidized product obtained after the experiments.The results showed that the obtained deoxidized product was a mixture of Ti and TiH 2 .This was because the residual Mgcontaining salt was not drained enough to expose the deoxidized product to a high p H 2 , as shown in Fig. 7a.When the residual Mg-containing salt was not sufficiently drained, the deoxidized product was covered with the residual Mg-containing salt, placing the deoxidized product at low p H 2 .As a result, although high p H 2 was maintained in the reaction system using an Ar and 20% H 2 mixed gas, the generation of Ti was inevitable.Therefore, to obtain pure TiH 2 , the residual Mg-containing salt should be sufficiently drained from the crucible after deoxidation.

Production of TiH 2 by hydrogenation
To produce pure TiH 2 by the hydrogenation of a mixture of Ti and TiH 2 obtained after deoxidation, various attempts were made to sufficiently drain the residual Mg-containing salt from the crucible.As shown in Table 1, the H 2 gas flow rates for deoxidation and hydrogenation, hydrogenation temperature, and mass fraction of MgCl 2 in MgCl 2 -KCl were varied, whereas the times for deoxidation, hydrogenation, and draining were fixed at 6 h, 24 h, and 3 h, respectively.
Figure 9 shows photographs of the remains inside the crucible after deoxidation, followed by hydrogenation.As shown in Fig. 9a,d, the deoxidized product in powder form was exposed to the atmosphere, unlike the case shown in Fig. 9b,c.These results indicated that the influences of an increase in the H 2 gas flow rate during hydrogenation and the hydrogenation temperature on the drainage of the residual Mg-containing salt were insignificant in these experiments, whereas a decrease in the mass fraction of MgCl 2 in MgCl 2 -KCl and an increase in the H 2  56 .This allowed the salt to exist as a liquid during hydrogenation at 773 K and to be further drained from the crucible during hydrogenation.In addition, when the H 2 gas flow rate during deoxidation increased from 300 to 500 sccm, the outflow rate of the fluid through the Ti mesh also increased during drainage.Therefore, the residual Mg-containing salt was further drained from the crucible, thereby exposing the deoxidized product to high p H 2 atmosphere.
Figure 10 shows the XRD analysis results of the deoxidized product obtained after HCl leaching.As shown in Fig. 10a-c, the obtained deoxidized products were identified as a mixture of Ti and TiH 2 .Unfortunately, although the deoxidized product was exposed to the atmosphere when the mass fraction of MgCl 2 in MgCl 2 -KCl was decreased from 0.75 to 0.55, the deoxidized products obtained were identified as a mixture of Ti and TiH 2 .This indicated that the residual Mg-containing salt should be more drained from the crucible to produce pure TiH 2 .However, Fig. 10d shows that the peak of the Ti phase diminished, and that TiH 2 was identified as the main phase in the obtained deoxidized product.This result indicates that the residual Mg-containing salt was sufficiently drained from the crucible when the H 2 gas flow rate during deoxidation was increased from 300 to 500 sccm.Consequently, the deoxidized product was exposed to high p H 2 , which enabled its hydrogenation.
Meanwhile, the O concentrations in the deoxidized products obtained after deoxidation followed by hydrogenation are listed in Table 1.As shown in Table 1, most of the results demonstrate that the O concentration was decreased to below 0.180 mass%.However, when the H 2 gas flow rate was increased from 300 to 500 sccm during deoxidation, the O concentration in the deoxidized product was 0.194 mass%, which is larger than 0.180 mass%.This was attributed to the use of a non-deoxidized Ar and 20% H 2 mixed gas.It is considered that using a purified Ar and 20% H 2 mixed gas is necessary to obtain pure TiH 2 and decrease the O concentration to below 0.180 mass%.
However, the results demonstrated that a decrease in the O concentration to below 0.180 mass% by deoxidation using Mg at high p H 2 was feasible, as expected from the thermodynamic analysis.Moreover, it was

Conclusions
The deoxidation process for off-grade Ti sponge using Mg with a wire mesh strainer type of crucible was developed with the aim of decreasing the O concentration to below 0.180 mass%, minimizing the loss of residual Mg-containing salt, and producing pure TiH 2 .After deoxidation using Mg in molten MgCl 2 -KCl salt at 933 K under an Ar and 20% H 2 mixed gas atmosphere for 24 h, the O concentration in the TiH 2 feedstock decreased from 1.28 mass% to 0.121 mass%.This result demonstrates that the O concentration can be efficiently decreased to below 0.180 mass% as expected the results of the thermodynamic analysis.The production of either a mixture of Ti and TiH 2 or pure TiH 2 was significantly influenced by the drainage of the residual Mg-containing salt from the crucible.As a result, pure TiH 2 was obtained by increasing the H 2 gas flow rate during deoxidation.Therefore, it was demonstrated that the minimal loss of residual Mg-containing salt and the production of pure TiH 2 by the deoxidation process developed in this study were feasible.

Figure 1 .
Figure 1.Flowchart of the deoxidation process for off-grade Ti sponge using Mg metal with a wire mesh strainer type of crucible in an Ar and 20% H 2 mixed gas atmosphere.

Figure 2 . 2 (
Figure 2. Chemical potential diagram of the Ti-O-H system at 973.15 K.

Figure 3 .
Figure 3. (a) Schematic of the experimental apparatus.Photographs of (b) the wire mesh strainer type of crucible, (c) TiH 2 feedstock, (d) stainless steel cap, (e) Ti mesh (100 mesh) at the bottom of the crucible, (f) TiH 2 feedstock and Mg inside the crucible, and (g) the crucible assembled with the stainless steel cap and tube.

Figure 4 .
Figure 4. (a) Schematic of the interior of the reactor at the hydrogenation step after drainage of the residual Mg-containing salt and (b) temperature profile measured along the vertical distance from the bottom of the reactor at 933 K before deoxidation.

Table 1 .
Experimental conditions and results of the deoxidation of TiH 2 feedstock.a Experimental conditions. 1) Weight of TiH 2 feed, w Feed = 10 g, Total weight of salt, w Salt = 200 g, Weight of Mg, w Mg = 10 g. 2) Temperature for deoxidation, T Deox = 933 K, Atmosphere: Ar + 20% H 2 .b Mass fraction of MgCl 2 in MgCl 2 -KCl was calculated using following equation: weight of MgCl 2 /(weight of MgCl 2 + weight of KCl).c Determined by N/O/H analysis using TCH600 by LECO corporation.

Figure 7 .
Figure 7. Representative photographs after the experiment: (a) residue inside the wire mesh strainer type of crucible, (b) residual Mg-containing salt under the Ti mesh at the bottom of the crucible, (c) cross-section of the salt collected inside the Fe container, (d) residue obtained after the first HCl leaching, and (e) residue obtained after the second HCl leaching.

Figure 8 .
Figure 8. XRD analysis results of the residues obtained after the experiments at the deoxidation times of (a) 1 h, (b) 3 h, (c) 6 h, (d) 12 h, and (e) 24 h.